Impregnating solutions



When introduced into the wood this solution will principally produce the following sub- PatentedJam 2, 1945 2,'366,612 U ITED- STATES PATENT" om'oe 1*. 1

2,366,612 IMPREGNATING SOLUTIONS Bror Olof Hager; Stockholm, Swedemassignor to Bolidens Gruvaktlebolas, Stockholm, Sweden, a limited stock company, of Sweden No. Drawing. Application July 28, 1942, Q

Serial No. 452,631

4Claims. (oi. rev-ass) The present invention relates to improvements in impregnating solutions for wood mother organic materials, more particularly to impregnating solutions of the kind described in my U. S. Patent No. 2,139,74'L'in which solutions chemical changes causing a precipitation of diflicultly soluble substances occur after .the introduction of the solutions into the material to be impregnated.

In order to give the idea of my invention a short description will be given of the principle diminish.

If any difllcultly soluble arsenate (e. g. zinc arsenate) is dissolved in a solution of arsenic and chromic acids and the solution is introduced into wood the zinc arsenate will be precipitated in the wood as a result of the acidity of the solution being reduced as the precipitation of the chromium arsenate proceeds.

In a solution of arsenic acid andchromic acid of the said composition (2HaASO4+2CIO3), containing about 0.4 per cent of Aszos, 3 mols of zinc arsenate .can be dissolved to every 2 mols of arsenic acid+2 mols of chromic acid. The resulting solution will contain about 1 per cent of A8205, which is theusual concentration for impregnating work. The solution will then contain the following substances:

When this solution is introduced into the wood zinc arsenate and chromium arsenate will be precipitated, principally according to the followin: formula:

stances.

1o s'zuaaoor+zcresor+snto+ao+zmci 'Ihe impregnating Solution 3 differs from som a tion]. primarily inthat it produces sodium chloride .in'the wood undergoing treatment.

so I i My u. s. lP-atent No.'2,1s9,'r4'z also states that theuse of easily soluble substances in the reparation of the impregnating solution is preferable tothe use of compounds that'are difficultly 5 soluble. The patent specification gives an instance of this, namely a solution containing the following substances in the .following propo'r tions:

The conversion of this solution in the "wood will principally produce the following substances: (6) 3ZnHASO4+2CrAsO4+4H20+30+3Na2SO4 The impregnating Solution 5 differs from Solution 1 primarily in that it produces sodium sulphate in the wood undergoing treatment.

a solution as in (5) above will generally give very satisfactory results. In practice however it ha often been found preferable to use more bichromate than prescribed above for the reason that bichromate is the key substance or the reaction and an excess of bichromate will consequently result in a more complete precipitation of the effective substances. The following examples illustrate this.

Pieces of wood'(l.5 by 2 by 5 cm.) were impregnated with a solution prepared according to Formula 5 and similar pieces with a solution of the same composition but with a surplus of ten per cent of NazCrzOv. The pieces were then subjected to leaching in running water and the amount of AS205 was determined. The following results were obtained:

per cent of original contents Ordinary Days of leaching solution I If the wood does not absorb the impregnating .fluid easilyan excess ofbichromate is partibest possible precipitation of the preservative substances in the inner layers or the wood. According to the present invention, more than 2 but less than 2.6 mols of'CrOa should therefore preferably be used to every 2 mols-0f HzAs04 in order to obtain satisfactory results.

oo If heat is applied'to speed up the impregnating cularly important in order to make sure of the Solution containing when the heat is applied, the zinc arsenate belng less soluble in hot than in cold solutions.

That will be shown by the following experiment.

Solutions containing zinc arsenate and bi- I chromate in different proportions have been heated and the temperature noted at which precipitation occurs in each case. The same experiments have been repeated with 1 g. or sugar dissolved in 250 cc. of the solution. This will make the solution less resistant to the action of the reducing substances that may be dissolved from the wood, as the sugar will eventually reduce the bichromate. In practice the solutions generally contain reducing agents leached from the wood. The experiments with the sugary solutions illustrate what is happening when such reducing agents are present in the impregnating solutions. The following results were obtained:

White precipitation at 67 C. N82CT207+2N82HASO+ 3H3AS04+3ZHS04 see compared with (2) The same solution with sugar Solution containing (The composition corresponding to 2ZnHAS04+2HaAS04+2CrO The same solution with sugar White precipitation at 64 O.

N o precipitation alter boiling hours White precipitation after boiling 14 min. Green precipitation after boiling 27 m n. The solution contains No precipitation after boiling Na2OrzO1+3H3AsO4+ZnSo 4 2 hours (The composition corresponding to ZnHAs04+2HaAs04+2CrOa) The same solution with sugar White and green precipitation after boiling 27 min.

Copper salts may also be used in equivalent quantities instead of zinc salts. The following experiments in heating copper solutions have been made.

(The composition corresponding to CuHASO4+2HaASO4+2CrO3 The same solution with sugar Precipitation at 59 C.

Precipitation at 56 C. Precipitation at 96 C.

Precipitation at 94 C.

Alter boiling 12 min. slight precipitation occurred. which was not increased by 2 hours boiling After boiling 8 min. a slight precigitation occurred. After precipitation occurred.

Aluminium salts may also be substituted for oiling 17 min. heavy (The composition corresponding to 2AlAsO +2HaAs04+2CrOr White precipitation at C.

White precipitation at 70 C.

The same solution with sugar Solution containing Na2Cr|O1+ NflzHASOr-I- White precipitation at 78 0 2%HzASO4 MAMSOU; (The composition corresponding to (A1A.$04+2HzAS04+2Cf0z) The samesolution with sugar Instead of dizinc-, dicopper-, or trialuminium arsenate other arsenates of these metals can be used in solutions described above.

Other diificulty soluble arsenates may be used for the'same purpose, e. g. the, arsenates of calcium, magnesium, barium, cadmium or the like.

In practice the solutions are best prepared from easily soluble substances as described in my U. s. Patent No. 2,139,747. The solution described above may for instance be prepared from alkali bichromate, arsenic acid, alkali arsenate and zinc sulphate (copper sulphate, aluminium sulphate) or other soluble compounds. Examples of solutions of such composition are the solutions used in the experiments described above to investigate the resistance to heating.

Having thus described my invention I declare that what I claim is:

1. An aqueous solution for impregnating'wood or other organic materials, said solution containcontaining between 1 and 3 mols or ZnHAsCM and between 2 and 2.6 mols of CrOa to every 2 mols or H3AsO4.

3. An aqueous solution for impregnating wood or other organic materials as claimed in claim 1, containing between 1 and 3 mols of CUHASQ4 and between 2 and 2.6 mols of CrOa to every 2 mols of HaAsOr 4. An aqueous solution for impregnating wood or other organic materials as claimed in claim 1, containing between 1 and 2 mols of AlAsO4 and between 2 and 2.6 mols of C10: to every 2 mols or H3A504.

BROR OLOF HAGER.

White precipitation at77 C.

t CERTIFICATE OF CORRECTION. H Patent no. 2,566,612; -J'an ua;'y 2, 191 BROR OLOF HAGER. V

It is hereby certified that error appears in the printed 'apecificefl on of the above numbered patent requiringcorrectiqn as follows; Pagel firat colunin, line for that portion of the formula read1ng"'2CrSe0 read --2CrAsO page 2, first coliunn, 1i n'es 2 9, 14.9 and. 53 and second'column,

line 9, after "20117 insert a closing parenthesis; same page, first column,

line 35', for "ZnSbe) read --ZnSO and thahthe said Lettere Patent should be read with thiscorrection' thereiri that th esame may conform to v the reeord of the case in the Patent Office;

Signed and sealed; this 15th day 51" ma A. 1).. 1915.

Leslie Fraz er (Seal) Acting Commissioner of Patents, 

